A vehicle transportation system may include multiple vehicles that travel on the same routes. The vehicles may have different characteristics, such as power outputs and weights, that affect how quickly the vehicles can navigate through the routes. A trailing vehicle traveling along a given route may reduce the distance between the trailing vehicle and a vehicle ahead along the same route that travels slower. The trailing vehicle has an incentive to reduce the total trip time in order to meet a designated arrival time at a destination, improve fuel economy, reduce emissions, and the like. However, if the trailing vehicle travels too close to vehicle ahead, the trailing vehicle may be required to slow to a stop for a designated period of time in order to avoid a risk of an accident between the two vehicles. The stop is undesirable as it may result in a significant delay and reduce fuel economy.
At least some of the routes over which vehicles travel may cross routes of other transportation systems, such as where rail tracks and road or highway systems cross over each other. To warn the vehicles of the other transportation systems, a vehicle approaching a crossing may be configured to activate a warning sound that is audible to people and animals near the crossing. Typically, the operator of a vehicle controls the warning sound in addition to other duties of the operator. It is not uncommon for the operator to make mistakes, such as to forget to activate the warning sound at the proper time, to activate the warning sound when not warranted (e.g., when the vehicle is in a quiet zone), or the like.